Conventionally, a heat exchanger such as a radiator has tubes and a header tank that communicates with the tubes. The header tank has a tank body made of resin and a core plate made of metal, and the tank body and the core plate are coupled. A gasket is adhered to the tank body to seal a clearance between the tank body and the core plate.
The gasket is made of a gasket material, which constitutes a liquid silicone-rubber composition, and is molded by injection molding in a state where an adhering portion between the tank body and the gasket is disposed in a mold. The silicone rubber composition contains a base resin, a crosslinking agent, a curing catalytic agent, a silane-coupling agent that is an adhesion auxiliary agent, and a silica filler.
Generally, it is known that there are two kinds of silica fillers, which are a hydrophilic silica filler and a hydrophobic silica filler. According to studies conducted by inventors of the present disclosure, a hydrophilic silica filler is more appropriate for the gasket material than a hydrophobic silica filler. The reason is that a compression set of the gasket can be smaller and a sealing effect by the gasket can be improved with a hydrophilic silica filler rather than a case where a hydrophobic silica filler is used. The compression set is, in other words, a residual distortion that occurs when the gasket is kept being compressed for a specified time period.
However, when the gasket material contains a hydrophilic silica filler, and when the gasket material is divided into two liquid materials to be stored separately, there may be a possibility of a following abnormality. Here, one of the two liquid materials contains the base resin, the hydrophilic silica filler, and the curing catalytic agent, and the other one contains the base resin, the hydrophilic silica filler, the crosslinking agent, and the silane-coupling agent. When the gasket is made of a mixture of the two liquid materials after storing the two liquid materials separately for a long time, an adhesive strength of the gasket with respect to the tank body made of resin decreases. Particularly, if the tank body is made of resin that is hardly adhered to a silicone rubber, an adhesive strength between the gasket and the tank body may be insufficient, and an adhesive failure may be caused between the gasket and the tank body.